Piñon and drought

[T]his episodicity was driven not by natural population processes but by the progression of strong decadal wet and dry regimes, as evidenced by the tree ring data. During pluvial events (pluvial is the opposite of drought), abundant soil moisture promoted pinyon germination and seedling survival. Soil moisture is critical at these developmental stages. Decadal-scale climate variability might have also regulated pinyon pine expansion through its effects on seed masting, the abundance and activity of animal dispersers, or even the movements of Native Americans (pine nuts were a staple food).